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Mounds View Stormwater Pond Assessment 1 INTRODUCTION July 2023 1 INTRODUCTION The City of Mounds View (City) contracted with Stantec to conduct a stormwater pond assessment to identify maintenance actions as part of its Stormwater Maintenance Program. This assessment would provide the City with information to better understand the current condition of its ponds and plan accordingly for recommended maintenance actions. This also provided an opportunity for the City to gather missing pond survey data and provide recommendations for operational practices to maximize their effectiveness. The project was initially planned to evaluate 31 basins. Beyond the required maintenance of the ponds, Stantec will use this information to provide recommendations to the City for enhancements to improve the function and aesthetics of selected ponds as well as to restore vegetation surrounding the ponds to improve aesthetics and create recreational and educational opportunities. 1.1 BACKGROUND Stormwater ponds are an important tool for managing runoff and water quality in urban areas. Ponds collect runoff and retain pollutants from impervious surfaces and stormwater networks and have the potential to improve water quality through sedimentation and nutrient cycling. Traditional wet ponds, also known as flow -through ponds, provide treatment by holding water equal to the volume of the permanent pool and allowing settling to occur. The permanent pool volume is the volume between the pond's normal water level (NWL) and true pond bottom. The water stored in the pond is later displaced by new runoff. Wet sedimentation basins have a combination of permanent pool storage and extended detention storage above the permanent pool to provide additional water quality or rate control. Dead storage is the volume below the outlet pipe elevation. Infiltration basins are designed to mimic a site's natural hydrology and temporarily store stormwater before allowing it to infiltrate into the soil. Infiltration basins do not have a permanent pool. Detention basins, or dry ponds, have no permanent pool, rely on extended detention storage, and are used primarily for rate control. (Minnesota Stormwater Manual, 2017) Pond maintenance is key to ensuring ponds serve their intended purpose, but many ponds are constructed with little or no follow-up maintenance. This lack of maintenance leads to sediment accumulation that can lower the water storage capacity of the pond and reduce total phosphorus (TP) and total suspended solids (TSS) retention efficiencies. 1.2 PROJECT APPROACH The project was divided into the following tasks and an overview of each task is provided below. A more detailed explanation can be found in Section 2 - Methods of this report. • Task 1: Basin surveys and inspections o The surveys collected basin bathymetry, basin -associated infrastructure (inlets and outlets), sediment accumulation, and surrounding topography at each site. The data collected in this task was the basis for much of the analysis in later tasks.